The present invention relates to a method for the production of crude oil from subterranean, oil-bearing formations comprising at least the following steps of providing an aqueous surfactant composition comprising water and a surfactant mixture, injecting said surfactant composition into the subterranean, oil-bearing formation through at least one injection well, thereby reducing the crude oil-water interfacial tension to less than 0.1 mN/m, and withdrawing crude oil from the formation through at least one production well, wherein the surfactant mixture comprises at least a surfactant (A) having the general formula R1—O—(CH2CH(R2)O)a-(CH2CH(CH3)O)b— (CH2CH2O)c—R3—Y− M+ (I) and a solubility enhancer (B) having the general formula R4—O—(CH2CH(CH3)O)x—(CH2CH2O)y—R3—Y− M+ (II), wherein R1 to R4, a, b, c, x, y, Y and M have the meaning as defined the the description and claims. The invention further relates to said aqueous surfactant composition and methods for preparing the same as well as the use of solubility enhancer (B) for enhancing the solubility of anionic surfactant (A).